Exploiting texture to estimate the relative intensities of overlapping reflections

Abstract

Abstract. Additional information about the relative intensities of reflections that overlap in a powder diffraction pattern can be obtained from a polycrystalline sample in which the crystallites are preferentially oriented. If the data are collected and analyzed appropriately, more single-crystal-like reflection intensities can be extracted, and thereby more complex structures solved. This 'texture method' was implemented initially in reflection mode and its power demonstrated with the solution of the 117-atom structure of the high-silica zeolite UTD-1F. However, the experiment required a minimum of 3 days of synchrotron beamtime per sample. In an attempt to reduce the amount of beamtime needed and to simplify the experiment itself, a transmission mode alternative using an area detector was developed. Details of the sample preparation, data collection and data analysis for both geometries are described. The solution of the structures of the aluminophosphates Mu-9 (R 3 3c, a ¼ 14.0696(1) A, c ¼ 42.3113(4) A) and AlPO-M (Pbca, a ¼ 9.7493(1) A, b ¼ 29.1668(2) A, c ¼ 9.3528(1) A) using reflection and transmission mode data, respectively, are provided as examples of the method.

Structure determination of the zeolite IM-5 using electron crystallography

“…The method presented here is especially useful for crystals that are too small, samples that are not pure, or zeolites with complicated structures. A.: A rational design of alkyl-aromatics dealkylation-transalkylation catalysts using C 8 Table S3. Final atomic position compared with the position refined by X-ray powder diffraction.…”

“…Several novel approaches such as incorporating crystal chemical information (FOCUS) [3,4], using pore/channel information to generate structure envelopes [5,6], or using textured samples to generate more singlecrystal-like data [7,8] have been developed for this purpose. However, when the structures become too complex and a large portion of the reflections overlap in the powder diffraction pattern, structure determination from X-ray powder diffraction data alone is very difficult.…”

Crystal Structures from Powder Diffraction: Principles, Difficulties and Progress

“…Several ideas were developed to assist (and improve) the extraction of integrated intensities from the powder pattern: those where no additional data must be collected, like the Patterson function (Chapter 12 in [3]), triplet relation based (Chapter 11 in [3]) or maximum entropy related (Chapter 14 in [3]) and those based on multiple datasets, like texture and thermal dilatation based (Chapter 9 in [3] and [21]). …”

“…Intense development of PM methods was started by zeolite research [26]. The texture method for integrated intensities extraction was developed on zeolite samples [21]. A nice topology-guided dual space method has been developed for zeolites [28], but the approach is easily modified to any other class of compound with a typical underlying topology.…”

Powder crystallography on macromolecules

“…Varying the temperature of the sample for low-symmetry unit cells often leads to anisotropic thermal expansion, and therefore allows overlapped peaks to be untangled (Shankland et al, 1997;Brunelli et al, 2003). Similarly, if a sample can be prepared with a significant degree of preferred orientation, then overlapped peaks will have different intensities depending on the orientation of the sample (Dahms & Bunge, 1986;Bunge et al, 1989;Cerny, 1996;Baerlocher et al, 2004). Combining multiple data sets together, where either the cell parameters or the preferred orientation are different, gives some information about the way in which the overlapped peaks should be partitioned.…”